In Norse myth, the defensive fortress which the gods build about the middle portion of the earth allotted to men in order to protect mankind from the giants.
Midgard (“middle world”) is on the same level as Nidavellir (land of the dwarfs), Svartalfheim (land of the dark elves/dwarfs) and Jotunheim (the land of the giants).
view the original article by Micha F. Lindemans at the Encyclopedia Mythica™
http://www.pantheon.org/articles/m/midgard.html